The present invention relates to an ignition system as disclosed, for example, in DE-OS No. 25 49 586. This type of circuit operates satisfactorily, but it would be desirable to provide some protection for the ignition transistor against overvoltages while it is in the blocked state, that is while a spark is being generated. Such a protection could comprise a clamping circuit which allows a switching of the ignition transistor to the conductive state for a short time while the spark is being generated, so that dangerous overvoltages would be substantially decreased. This is, however, difficult to accomplish in the known circuit since the current limiting resistor would then immediately cause the auxiliary transistor to become conductive causing the current flowing through the clamping circuit to flow through the emitter-collector circuit of the auxiliary transistor. Under these conditions, a collector-base clamping circuit for the ignition transistor would no longer be effective and the auxiliary transistor could be destroyed by excessive currents.